$ 10^{-10}$
Explanation: $= \left(\dfrac{1}{10}\right)^{10}$ $= \left(\dfrac{1}{10}\right)\cdot\left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)$ $= \dfrac{1}{100}\cdot\left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)$ $= \dfrac{1}{1000}\cdot\left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)$ $= \dfrac{1}{10000}\cdot\left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)$ $= \dfrac{1}{100000}\cdot\left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)$ $= \dfrac{1}{1000000}\cdot\left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)$ $= \dfrac{1}{10000000}\cdot\left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)$ $= \dfrac{1}{100000000}\cdot\left(\dfrac{1}{10}\right)\cdot \left(\dfrac{1}{10}\right)$ $= \dfrac{1}{1000000000}\cdot\left(\dfrac{1}{10}\right)$ $= \dfrac{1}{10000000000}$